//--------------------------------------------------------------------------
// $Id: DHKeyPair.java 10 2006-08-21 13:48:09Z zendragon $
//--------------------------------------------------------------------------
// Copyright 2006 Social Brain Foundation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//--------------------------------------------------------------------------

package org.socialbrain.openid.security;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import java.math.BigInteger;
import java.util.Random;

/**
 * @author <a href="http://erning.net/">Zhang Erning</a>
 * @version $Id: DHKeyPair.java 10 2006-08-21 13:48:09Z zendragon $
 */
public class DHKeyPair
{
    public DHKeyPair(BigInteger modulus, BigInteger gen, BigInteger privateKey)
    {
        _modulus = modulus;
        _gen = gen;
        _privateKey = privateKey;
    }

    public DHKeyPair(BigInteger modulus, BigInteger gen)
    {
        _modulus = modulus;
        _gen = gen;

        Random random = new Random();
        int bits = random.nextInt(modulus.bitLength());
        byte[] bytes = new byte[bits / 8];
        random.nextBytes(bytes);

        _privateKey = new BigInteger(bytes).abs().mod(_modulus.subtract(BigInteger.ONE)).add(BigInteger.ONE);
    }

    public BigInteger getModulus()
    {
        return _modulus;
    }

    public BigInteger getGen()
    {
        return _gen;
    }

    public BigInteger getPrivateKey()
    {
        return _privateKey;
    }

    public BigInteger getPublicKey()
    {
        if (_publicKey == null)
        {
            _publicKey = _gen.modPow(_privateKey, _modulus);
        }
        return _publicKey;
    }

    public BigInteger computeSecretKey(BigInteger peerPublicKey)
    {
        return peerPublicKey.modPow(_privateKey, _modulus);
    }

    private BigInteger _modulus;
    private BigInteger _gen;
    private BigInteger _privateKey;
    private transient BigInteger _publicKey;

    private transient static final Log _logger = LogFactory.getLog(DHKeyPair.class);
}
